1. Field of the Invention
The present invention relates to a fuel injection controller that diagnoses an injection quantity of a fuel injection valve that injects fuel to a cylinder of an internal combustion engine.
2. Description of Related Art
Recently, in order to meet the more strict emission control regulation, there has been a need for highly accurately control of an injection quantity of a fuel injection valve. For example, during one combustion cycle of a common-rail diesel engine, a pilot injection with a minute injection quantity is performed before a main injection that causes main torque for the engine. In the above case, the injection quantity is required to be highly accurately controlled Thus, mechanical improvement has been made in order to deal with machining error or age deterioration of the fuel injection valve.
However, because there is limitation in the mechanical improvement, as shown in JP-A-2005-36788 corresponding to US2004/0267433, the injection quantity is learned in order to correct the injection quantity such that the injection quantity of the fuel injection valve is highly accurately controlled. In the above injection quantity learning operation, a drive signal used for commanding the fuel injection valve to inject fuel is corrected by a correction amount that is determined based on a difference between a command injection quantity and an actual injection quantity. The command injection quantity is a target quantity of fuel required in the operation, and the actual injection quantity is an actual quantity, by which the fuel injection valve actually injects fuel.
For example, the injection quantity learning operation is executed when the internal combustion engine has been operated for a certain operational time period, or when the vehicle travels certain travel distance. If the learning operation is executed based on the above execution condition, sliding performance deterioration or wear of the fuel injection valve may develop more than expected before the next injection quantity learning operation is executed. As a result, the difference between the command injection quantity and the actual injection quantity may widely exceed a predetermined range finally. In other words, the above abnormality of the injection quantity will not be detected until the next injection quantity learning operation is executed. Thus, toxic substances in the exhaust gas may be emitted at a level beyond the legal limit disadvantageously.
Also, when the difference between the command injection quantity and the actual injection quantity becomes greater than the predetermined range, a correction amount, which is used for correcting the drive signal, and which is computed based on the difference between the command injection quantity and the actual injection quantity, may also exceed a correction limit value, accordingly. For example, when the correction amount is equal to or less than the correction limit value, it is possible to accurately correct the injection quantity based on the correction amount such that the actual injection quantity substantially becomes the command injection quantity. However, when the correction amount is greater than the correction limit value, it may not be assured that the injection quantity is accurately corrected based on the correction amount. Thus, when the correction amount goes beyond the correction limit value, it is difficult to highly accurately compute an uncorrectable deviation amount between the command injection quantity and the actual injection quantity based on the correction amount of the drive signal. In the above, the uncorrectable deviation amount corresponds to a deviation amount between (a) the command injection quantity and (b) the actual injection quantity made based on the drive signal that is corrected by the correction limit value serving as the correction amount.